The invention relates to a spring hinge for glasses with a central part and with side pieces wherein the hinge element is guided for displacement.
Spring hinges of the type mentioned here are known. They serve for connecting the lens-containing central part of a pair of glasses in a flexibly resilient manner to the side pieces. The side pieces can be displaced from a first functional position, in which they butt against the central part, into a second functional position, in which they run approximately at right angles to the central part. If the side pieces are pivoted outward beyond the second functional position, a spring device in the spring hinge is activated, and this spring device draws the side pieces back into the second functional position. For improved usage of the glasses, it is possible, for the purpose of putting the glasses on, for the side pieces to be pivoted outward beyond the second functional position and thus be overflexed. The spring device of the spring hinge is thus activated, to be precise such that the side pieces are drawn back into the second position. The spring device thus also causes the side pieces to be pressed against the wearer's head when the glasses are being worn, with the result that the glasses grip better.
Overflexing of the side pieces activates the spring device, with the hinge element being drawn some way outward out of the housing of the spring hinge counter to the restoring force of the spring device. This displacement of the hinge element requires guidance. In conventional spring hinges, the hinge element is inserted, together with the spring device, into a cavity which is introduced into the housing. Regions of the cavity interact with the hinge element such that a guide region is formed. This guide region serves for reliably guiding the hinge element as it is displaced and for preventing relative rotation between the housing and hinge element. The cavity, which on the one hand accommodates the spring device and the hinge element and on the other hand has guide regions, has to be of relatively long design in order for it to be possible to realize the guide regions wherever there is no spring device present. As seen over the length of the cavity, there are thus sections in which the spring device is arranged and further sections which form the guide region.
Spring hinges are preferably to be used more and more frequently in order to increase the wearing comfort of glasses. Since the glasses frames, in some models, are intricately formed, the spring hinges have to be very small. The fact that the cavity in the housing has to have sections for the spring device and for the guide region inevitably give rise to a relatively long construction of the housing and thus of the spring hinge. It is thus not possible to use the latter in some cases.